Unfortunately conditional dropdowns are only accessible through a relationship/table type setup. I would advise that instead of using a generic text-multiple choice with shared values that you create a table of those options and have your users pick from that table accordingly. That is the only way to dynamically update the list of options in a dropdown on a record by record basis.
Ok, when I build the table with the additional options how do I create the condition for the new related field to only show certain options based off of choices in another reference field?
In this additional table you will need to include a field that is associated with the first reference field. So for example let's say your first reference field is 'Status' and the second Reference field is now 'Sub-Status'. In your first dropdown you'll have options like the below for Status:
Not Started
In Progress
Complete
Now in your second table - you need a field for 'Sub-Status' but you also need to note the Status that it goes with and thats the binding element in your conditional dropdown. So your sub-status table might look like:
Status Sub-Status
Not Started Bids Pending
Not Started Pending Approval
Not Started Pending Signature
In Progress In Development
In Progress Final Validation
Complete Invoice Pending
Complete Closed
Your new table needs to have a field that actually references your first value
